(31 May 2015, 7:29 pm)R838PRG wrote The Current Scheme was started in 1975 and is no where near used up 40 years later, so would imagine it would take at least another 40 years to fill.
I am aware that it will take many more years to complete the system but it will end eventually. It was just a general question to be thought about for the future and not to be answered properly.